This invention relates to a calibrating fluid for automated blood cell counting instruments.
The use of automated blood cell counting instruments in hematology is well known. In general, these instruments employ one or the other of two types of particle size analyses. In one type, each particle is counted and its discrimination property is measured directly. In the other type, the particles are measured in bulk and particle behavior is recorded through a series of measurements of the magnitude of the bulk, in terms of the count, combined surface area or combined mass. The type of measurement used then determines the basis of the size distribution.
Optical and electrical properties are two of the most prevalent types of size discriminating properties employed in these particle size analysis instruments. The optical equipment generally employs imaging, spectral transmission, scattering and diffraction mechanisms, while the electrical equipment usually employs resistance, capacitance, and charge mechanisms.
In addition to the counting of blood cells, the more sophisticated automated blood cell counting instruments provide determinations of other blood values such as hematocrit and hemoglobin values. Because of its characteristic red color, hemoglobin lends itself to colorimetric determinations. This gives rise to the use of a colorimeter unit on various blood cell counting instruments.
Various methods of hemoglobin determination which are generally employed in these automated instruments are the cyanomethemoglobin technique and the oxyhemoglobin method. In the former technique, the blood specimen is diluted with a reagent containing ferricyanide and cyanide, which converts both reduced hemoglobin and oxyhemoglobin to the cyanomethemoglobin form. The absorbance of the cyanomethemoglobin at 540 m.mu. is then used for quantitation. In the latter method, the blood specimen is diluted with an aqueous solution tetrasodium salt of ethylenediamine tetraacetic acid (EDTA) and mixed with air to convert hemoglobin to oxyhemoglobin. The absorbance of oxyhemoglobin at 540 m.mu. is then measured.
Notwithstanding the general reliability of commercially available automated blood cell counting instruments, test values obtained with these instruments are only as accurate as the operator's technique and understanding of the instrument. In the absence of stringent control programs, together with regular recalibration of the instruments, one cannot always be assured of correct results. Experience has shown that quality control in the application and use of these automated blood cell counting instruments is a necessity for good hematological practice.
In the case of some types of automated blood cell counting instruments, the use of fresh whole blood in calibrating the instrument is a very cumbersome procedure, requiring approximately 2 hours to calibrate the instrument. When using the reference control blood supplied by the manufacturer of these instruments, values recorded under "mean value" in the assay instruction sheet are set on the instrument after the reference control blood has been allowed to cycle through the machine. In other words, values recorded on the reference control blood are used to calibrate the machine. It has been found in these instances that when a hematocrit which has been reported at 47.3, for example, on the assay instruction sheet is actually spun in a centrifuge, it does not give an answer of 47.3, but gives an answer of 27-30. Therefore, the reported value is not a true hematocrit. In reporting the hematocrit values, the numbers are given with reference to the specific type of machine used for the determination, which further indicates that this is not a true hematocrit. Thus, the importance of calibrating the machine correctly cannot be overstressed.
Among the reference control blood systems used for calibrating blood cell counting instruments are the semi-fixed systems in which the cells are lightly tanned either with formaldehyde, gluteraldehyde, or tannic acid. By this procedure, the outer membrane of the red blood cell has been fixed so that it cannot swell, although the cell can shrink. If the value which the manufacturer of the blood cell counting machine has placed on the assay instruction sheet is not correct and operators are setting this value into the machine and cycling presently-available calibrating solutions into the machine, it will appear that the calibrating solution has swollen more than is actually the case.
Other known reference control systems for automated blood cell counting instruments are described in U.S. Pats. Nos. 3,558,522; 3,705,110 and references cited therein.
The need for accurate color standards in clinical hemoglobinometry to establish the relation between instrument readings and concentration of hemoglobin in unknown samples is further set forth in various publications, for example, the paper by Cannan, Amer. J. Clin. Path., Vol. 30, pp. 211-215 (1958).
Accordingly, it is an object of this invention to provide an improved calibrating fluid for automated blood cell counting instruments.
It is a further object of this invention to provide an improved calibrating fluid for automated instruments, used for blood cell counting and hemoglobin determinations.
Other objects and advantages of the invention will be apparent to the person skilled in the art after reading the present specification and the appended claims.